Puzzled 2

[Sark1]

I am religious about no thyroxine before blood test but I too have wondered how since it takes about 6 weeks to get results when starting levothyroxine you get an instant result affecting blood tests by omitting a dose. Having said that on the days that I take a raised dose I feel better!

[startagaingirl]

Hi - it takes 6 weeks to get full effects from levothyroxine because first your body has to convert it to the active form T3, this is predominantly done in liver. This is then followed by your body reacting to this T3 by opening up receptors in every system of your body that had previously been set to dormant status by a lack of T3. This happens when your body progressively shuts or slows down any systems that are not essential to keeping you alive. This joint process takes about 6 weeks to reach the maximum effect, hence the requirement to wait 6 weeks between tests and dose increases. Why you shouldn't take a dose in the 24hrs before your test is because the level of T4 in your blood is one of the tests normally done. If you have recently taken a dose this will only reflect the rate at which your body dissolves the tablet and transfers it into your blood. Whereas what is actually required is the baseline level that is normally retained as "spare" in your blood and hence available for your body to convert as required.

Hope that helps and isn't as clear as mud!

Gillian

[Sark1 in reply to startagaingirl]

Good answer! That will keep me quiet for a while!

[shaws Administrator in reply to startagaingirl]

Brilliant answer